A differential device installed in a vehicle includes a differential case that is rotatably housed inside a transmission case through bearings. Inside the transmission case, a drive pinion gear driving the differential case is rotatably housed, and the drive pinion gear is fixed on the outer side of the differential case so as to mesh with a final driven gear.
The differential case includes built-in parts, such as a pinion gear, a pinion shaft, and a side gear, a pair of inboard shafts that distribute a driving torque from the final driven gear to the outside, and inboard parts with a spiral oil guide groove that rotatably support the inboard shafts inside the transmission case. In a lubricating structure for such a differential device, it is important to maintain the inboard parts, the inside of the differential case, and the bearings supporting the differential case in a well-lubricated state.
Generally, lubricating oil is retained in a bottom part of the transmission case, and as the final driven gear scoops up, while agitating, the lubricating oil when the vehicle is traveling, the inside of the case is maintained in a lubricated state. There is a known lubricating structure having a guide groove which is formed in the inner surface of the transmission case and through which lubricating oil scooped up by the final driven gear is guided to the inboard parts and the bearings. Another known lubricating structure has bearing spacers and a guide plate provided on the outer side of the bearings, by which dripping lubricating oil is guided to the outer side of the inboard parts and the bearings (e.g., see Patent Literature 1).